Screw propeller and the like



A. B. STEWART SCREW PROPELLER AND THE LIKE July 6, 1937.

Filed Dec. 1, 1956 \hl l l l ll I ullllllllnilimwllllllnI. I

' "'IIIIII'I'A ""IIIII 23' Patented July 6, 1937 UNITED STATES rarest or ies In Great Brit 1 Claim.

This invention relates to screw propellers for propelling aircraft and marine vesselssuch as aeroplanes, airships, torpedoes, ships, boatsand to fans and impellersfor example, of hydraulic turbines-and to fishing tackle spinners; such propellers, fans, impellers, spinners and such like articles being referred to herein generally and in the claim by the term screw propeller.

An object of the invention is to make provision whereby the loss in efficiency of a screw propeller, due mainly to slip, is reduced and the thrust proportionately increased.

Another object of the invention is to reduce radial dispersion of the fluid (generally air or water) in which the propeller works and to concentrate said fluid within the tip circle of the blades and towards their axis of rotation, so that the work done by the blade will be distributed with comparative uniformity throughout the thrusting surface (i. e. the rear or aft surface) of the blade.

Another object of the invention, in so far as concerns a propeller to work in water, is to provide for concentration of the water within the circle of the blades in order to minimize production of air bubbles on the blade surfaces and accordingly to reduce the usual pitting of said surfaces.

Another object of the invention is to provide a propeller whereby a craft or vessel or the like is enabled to thrust powerfully against head seas, gales, head winds and other forms of external resistance, and whereby control of the craft or vessel is facilitated, and whereby its stability and ability to accelerate are enhanced, these properties being especially valuable in the case of heavier-than-air aircraft as regards taking-01f and landing, and whereby vibration and noise are minimized.

Towards the attainment of the foregoing objects, provision is made whereby the fluid is deflected inwardly (i. e towards the propellers axis of rotation) over a large proportion of the blade 5 area. The screw propeller has a blade which is so formed that its approximate medial line is concavely curved with reference to the blade edge which leads in the ahead or normal direction of rotation of the blade, and the blade tip is pro- 50 vided with a fin which is much shorter than the maximum blade width, is set perpendicularly on the blade and is arranged wholly or largely in advance of the approximate medial line.

Fins such as hereinbefore described may con- 55 veniently be termed burrowing tips on account ain June 8, 1935 of their burrowing or scooping action on the fluid. Preferably, the blade is formed with a concavely curved edge which leads in the ahead or. I

normal direction of rotation of theblades; i. e. a leading edge curved in the manner of the cutting edge of a scythe.

The invention referred to in the foregoing statements will now be more particularly described by way of example with reference to the accompanying diagrammatic drawing, in which:

Fig. 1 is a rear elevation of a single blade of a ships propeller. I

Fig. 2 is a'fragmentary sectional View corresponding to Fig. l but drawn to a larger scale. i

Figs. 3 and 4 are fragmentary sections on the planes III and IV of Fig. 1, Figs. 3 and 4 being drawn to a larger scale than Fig. 1.

Figs. 5 and 6, which correspond to Figs. 3 an 4, illustrate a modification.

Figs. 7 and 8, which correspond to Fig. 3, illus trate further modifications.

Fig. 9 is a fragmentary section on the plane IX of Fig. 1, Fig. 9 being drawn to a larger scale than Fig. l.

Fig. 10 is a rear elevation of a single blade of a torpedo propeller, and Fig. 11 is a section, drawn-to a larger scale, on the plane XI of Fig. 10.

Fig. 12 is a rear elevation of a single blade of an aerial propeller, Fig. 13 is a vertical section at right angles to Fig. 12 and Fig. 14 is a section, drawn to a larger scale, on the plane XIV of Fig. 12. Fig. 15 is a cross-sectional view taken on the line l5-I5 of Figure 1.

Referring to Figs. 1 to 4, the ships propeller blade therein illustrated is formed with a concavely curved leading edge 2ilthat is, the edge which leads in the ahead or normal direction of rotation of the blade denoted by the arrow A, Fig. 1the curvature resembling somewhat that of the cutting edge of a scythe. The trailing edge 2| of the blade is curved convexly, said edge rounding slowly into the tip. The blade is provided at its tip with a fin 22 arranged adjacent to the dot-dash line B denoting the tip circle of the blade. The fin 22 is arranged on theaft face of the blade, but it may project more or less forwards if desired, as in the modification according to Figs. 5 and 6. As shown, the fin in general,- and its radially inner face in particular, are arranged perpendicular to the blade face. The fin 22 when viewed radially may be of substantially triangular form, with a short side 23 leading and a long side 24 trailing, and the long side may be' straight as shown in Fig. 3, or arched as shown at 2 3 in Fig. 7. Conversely, as shown in Fig. 8, the arrangement may be such that the long side 24 leads and the short side 23 trails, the long side being either straight, as shown, or arched.

The blade is of airfoil form in cross-section and the fin is also of such form on its radially outer surface, its inner surface being arcuately divergent from the tip circle B in order to deflect and guide the water inwards towards the axis of rotation. 1

The approximate medial line of the blade is denoted by C, the line being shown extending throughout most of the blade length, but stopping before reaching the tip, because there the trailing edge 2? deviates rapidly from its general curvature at maximum blade width and therefore the general direction of mediality no longer persists in proximity to the tip. It will be seen that the line C is ccncavely curved with reference to-i. e. as viewed fr0m-the leading edge and that the fin 22 lies almost entirely to the leading side of the medial line C. Thus, the water deflected inwards by the fin causes concentration of water on the main portion of the blade area.

The leading edge 26 merges in a convex curve into the tip, this curve being provided chiefly to reduce the risk of fouling of the propeller by weeds, ropes or loose fioating matter; and the inclined leading edge 23 of the fin 22 is provided chiefly for the same purpose.

The blade shown is provided with a scooplike formation 25, Figs. 1 and 9, arranged to project forwards from the leading edge at a material distance from the blade tip. Such a formation serves to guide the fluid gathered by it across the rear face of the blade, and accordingly any tendency of the fluid to disperse radially is still further reduced. There may be more than one formation such as 25 at diiferent distances from the blade tip.

The aerial propeller blade illustrated in Figs. 12, 13, and 14 is composed of a metal body 38 faced with wood 3i, such for example as balsa wood laminae, although the Wood may be replaced by other light material and the metal of the body may be wholly or partially replaced by hard wood. The fin 22 is formed in the body.

The blades according to Figs. 10-14, and other propellers and the like according to this invention, are based upon the same principles as the blade described with reference to Figs. 1 to 4 and are subject to the same modifications, the proportions and constructions in each instance conforming in general to the requirements involved in the particular use to which the propeller or the like is to be put.

Although the invention has been described with reference to a single blade, it will of course be understood that this has been done for simplicity of description and'illustration, and that the invention applies to propellers and the like having the usual numbers of blades.

The fin may as shown in the drawing be arranged fiush with the extreme tip of the blade or it may be arranged slightly inwards from the tip (the latter arrangement being preferable where the fin is secured to the blade by welding) to permit the outer face of the fin to merge into the blade tip in a reinforcing fillet serving to resist the radially outward force on the fin. I

The propeller blade may be of substantially constant pitch or lead from root to tip; although, if desired, the arrangement may be such that the pitch varies, for example decreases uniformly from root to tip.

3 Propellers for aircraft may have theblades made wholly or mainly of metal, in which event the fins may be cast or otherwise formed in the metal or attached thereto; or the blades may be made each with a light strong metal core or frame faced with or encased in wood, the fins in that event preferably consisting of projecting extensions of the cores; or the blades may be made wholly or mainly of wood.

Propellers or the like for uses other than for the propulsion of aircraft would as a rule be made wholly or mainly of metal.

I c1aim:--

In a screw propeller, a blade having a concavely formed leading edge and a trailing edge substantially of convex form, a medial line disposed therebetween, said medial line being offset from the plane of said edges and forming therewith a concave surface, a fin disposed at the tip end of said blade and lying at a right angle thereto, said I fin having its rear end terminating at a point adjacent the medial line of said'blade and its inner face curving inwardly from the leading edge of the blade so as to deflect the fiuid across the blade. 7

ARCI-HBALD BYERS STEWART. 

